In applications such as medical laboratory and process instrumentation, it is often necessary to provide precisely measured quantities of a sample, diluents, or reagents. For example, a very small quantity of sample, i.e. several microliters, might be diluted with several hundred microliters of buffer before being mixed with a quantity of reagent.
Very accurate dosages of sample, diluent, and reagent have traditionally been provided by fluid displacement pumps. Such pumps very accurately measure the quantity of fluid displaced. In order to measure fluid displacement accurately, it is necessary to have a precisely machined pump cylinder and piston and a precise mechanism for driving the piston to displace the fluid.
Typically, two different pumps are needed: one for the very small quantity of sample and another for the much larger quantity of diluent. Furthermore, it is typical for the precise driving mechanism to be off-axis from the cylinder and connected to the piston by some mechanical linkage such as pulleys and drive belts. Because the driving mechanism is off-axis, it may introduce substantial strain against the piston, leading to early failure due to wear on the pump seals.
There is a need for a fluid displacement pump which can accept pistons and chambers of varying size, depending on the quantity of fluid needed to be measured. Ideally, such a pump would be able to dispense both a large quantity of diluent and a tiny quantity of sample. Additionally, the pump should have a precision driving mechanism axially aligned with the cylinder and piston, in order to conserve space and reduce wear on the seals.